Cambridge-based Vertex Pharmaceuticals Inc.’s Kalydeco drug for cystic fibrosis was approved by Australian regulators. Kalydeco, cleared by US regulators in February 2012, targets the cause of the disease in about 4 percent of the US patient population — those with a specific genetic mutation — helping them produce mucus to absorb and digest food. Life-threatening CF affects about 70,000 people worldwide. In April, investors bid up Vertex shares to a record high after clinical data appeared to dramatically improve the prospects of Vertex’s plan to build a portfolio of CF drugs.